I wouldn't know the real reason for sure, but this seems plausible:
1) They got tired of having to modify C code and wait for the deploy cycle to modify the filter
2) Using, for example, the database would be more work than calling a shell script. On top of that, it might actually be beyond the abilities of the programmer involved.
3) The C code executes on an arbitrary machine. Hence the ssh to a specific machine, so that the shell script would only have to be maintained in one place
1) They got tired of having to modify C code and wait for the deploy cycle to modify the filter
2) Using, for example, the database would be more work than calling a shell script. On top of that, it might actually be beyond the abilities of the programmer involved.
3) The C code executes on an arbitrary machine. Hence the ssh to a specific machine, so that the shell script would only have to be maintained in one place